Compact EH Support

[Alan Modra]

On Fri, Sep 02, 2016 at 02:18:57PM +0000, Moore, Catherine wrote:
> The intent with the addition of _bfd_elf_section_for_symbol was to pull common code from bfd_reloc_symbol_deleted_p and bfd_elf_parse_eh_frame_entry.
> This patch adds the comment and updates bfd_reloc_symbol_deleted_p to call _bfd_section_for_symbol.
> OK to push?

No.

> 2016-09-02  Catherine Moore  <clm@codesourcery.com>
> 
>         * elflink.c ( _bfd_elf_section_for_symbol): Add comment.
>         Merge discard criteria from bfd_elf_reloc_symbol_deleted_p.
>         (bfd_elf_reloc_symbol_deleted_p): Delete common code. Call
>         _bfd_section_for_symbol.
> 
> diff --git a/bfd/elflink.c b/bfd/elflink.c
> index 9e9a33c..00603be 100644
> --- a/bfd/elflink.c
> +++ b/bfd/elflink.c
> @@ -58,6 +58,11 @@ struct elf_find_verdep_info
>  static bfd_boolean _bfd_elf_fix_symbol_flags
>    (struct elf_link_hash_entry *, struct elf_info_failed *);
> 
> +/*  Given a relocation cookie and its symndx, return the section
> +    that defines the symbol or NULL if the symbol is not defined.
> +    When DISCARD is true, a local symbol that has been defined in
> +    a discarded section will be treated as an undefined symbol.  */
> +

I'd be happy if the function were true to name and performed as per
the first two lines of your new comment.  But this is *not* what
_bfd_elf_section_for_symbol does.  Instead, for global symbols, it
only returns the section if the symbol is defined in a discarded
section, and it does so regardless of the parameter DISCARD.  That is
inconsistent with the treatment of local symbols, and probably a bug
in the use of the function by _bfd_elf_parse_eh_frame_entry.

>  asection *
>  _bfd_elf_section_for_symbol (struct elf_reloc_cookie *cookie,
>                              unsigned long r_symndx,
> @@ -92,8 +97,10 @@ _bfd_elf_section_for_symbol (struct elf_reloc_cookie *cookie,
>        /* Need to: get the symbol; get the section.  */
>        isym = &cookie->locsyms[r_symndx];
>        isec = bfd_section_from_elf_index (cookie->abfd, isym->st_shndx);
> -      if (isec != NULL
> -         && discard ? discarded_section (isec) : 1)
> +
> +      if (!discard
> +         || (isec != NULL
> +             && (isec->kept_section != NULL || discarded_section (isec))))
>         return isec;
>       }
>    return NULL;
> @@ -13509,40 +13516,8 @@ bfd_elf_reloc_symbol_deleted_p (bfd_vma offset, void *cookie)
>        if (r_symndx == STN_UNDEF)
>         return TRUE;
> 
> -      if (r_symndx >= rcookie->locsymcount
> -         || ELF_ST_BIND (rcookie->locsyms[r_symndx].st_info) != STB_LOCAL)
> -       {
> -         struct elf_link_hash_entry *h;
> -
> -         h = rcookie->sym_hashes[r_symndx - rcookie->extsymoff];
> -
> -         while (h->root.type == bfd_link_hash_indirect
> -                || h->root.type == bfd_link_hash_warning)
> -           h = (struct elf_link_hash_entry *) h->root.u.i.link;
> -
> -         if ((h->root.type == bfd_link_hash_defined
> -              || h->root.type == bfd_link_hash_defweak)
> -             && (h->root.u.def.section->owner != rcookie->abfd
> -                 || h->root.u.def.section->kept_section != NULL
> -                 || discarded_section (h->root.u.def.section)))
> -           return TRUE;

The code you're deleting here does not match the code in
_bfd_elf_section_for_symbol!

> -       }
> -      else
> -       {
> -         /* It's not a relocation against a global symbol,
> -            but it could be a relocation against a local
> -            symbol for a discarded section.  */
> -         asection *isec;
> -         Elf_Internal_Sym *isym;
> -
> -         /* Need to: get the symbol; get the section.  */
> -         isym = &rcookie->locsyms[r_symndx];
> -         isec = bfd_section_from_elf_index (rcookie->abfd, isym->st_shndx);
> -         if (isec != NULL
> -             && (isec->kept_section != NULL
> -                 || discarded_section (isec)))
> -           return TRUE;
> -       }
> +      if (_bfd_elf_section_for_symbol (rcookie, r_symndx, TRUE) != NULL)
> +       return TRUE;
>        return FALSE;
>      }
>    return FALSE;

It seems likely to me that you should delete "discard" from
_bfd_elf_section_for_symbol and any qualification of the section being
discarded, in the function.  Here you can then use

    isec = _bfd_elf_section_for_symbol (rcookie, r_symndx);
    return (isec != NULL
	    && (isec->owner != rcookie->abfd
		|| isec->kept_section != NULL
		|| discarded_section (isec)));

-- 
Alan Modra
Australia Development Lab, IBM